This application claims the benefit of Japanese Patent Applications No. 2002-025802 filed Feb. 2, 2002, No. 2002-075832 filed Mar. 19, 2002, No. 2002-081714 filed Mar. 22, 2002, No. 2002-211471 filed Jul. 19, 2002, No. 2003-015343 filed Jan. 23, 2003, No. 2003-015344 filed Jan. 23, 2003 and No. 2003-015345 filed Jan. 23, 2003, in the Japanese Patent Office, the disclosures of which are hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to image forming apparatuses, memory control apparatuses and memory control methods, and more particularly to an image forming apparatus which stores input images in a page memory and processes the stored images for printing, and to a memory control apparatus and a memory control method which are suited for such image processing.
2. Description of the Related Art
In image forming apparatuses having the functions of a digital copying machine, facsimile machine, printer and scanner, a page memory is provided between an image input/output end and a secondary storage unit such as a hard disk drive (HDD), so as to compensate for a relatively low transfer rate of the HDD by the page memory having a high access speed.
An input image data is temporarily developed in the page memory, and the developed input image data is transferred to the secondary storage unit such as the HDD. When outputting the image data, the image data stored in the HDD is developed in the page memory, and the developed image is output. Hence, the page memory functions as an intermediate buffer.
Recently, it has become necessary for the image forming apparatuses described above to process a color image data. As a result, the number of colors which need to be input and output has increased, and a page memory management has become complex. For example, it is necessary to output image data of magenta (M), cyan (C), yellow (Y) and black (K) which amounting to four times that of a black-and-white image data. For this reason, the page memory cannot be acquired for the image data input and output if the page memory management has discrepancies between the input and output, and it is impossible to input and output the image data in such a case. On the other hand, the page memory cannot have an extremely large storage capacity due to cost restraints, and there are demands to efficiently utilize the storage capacity of the page memory for the input and output of the image data or, at least for the output of the image data.
For example, a Japanese Laid-Open Patent Application No. 2000-253223 proposes an example of a method which improves the utilization efficiency of the page memory having a low utilization efficiency, by changing the image resolution. This proposed method judges whether or not the page memory overflows, and reduces the resolution by a resolution converting means if the page memory overflows. The image data having the reduced resolution is compressed and stored in the page memory, for use in forming the color image.
In addition to the image forming apparatuses provided with the secondary storage unit such as the HDD, there are image forming apparatuses having no secondary storage unit such as the HDD. In the case of the image forming apparatus provided with the secondary storage unit such as the HDD, it is possible to design the page memory control under a precondition that the page memory can be used if the image data can be saved in the HDD. But in the case of the image forming apparatus not provided with the secondary storage unit such as the HDD, there is no backup mechanism for the input image data, and the input image data must be stored in the page memory until the printing of the input image data is completed. Hence, the page memory can be used to store the next input image data only after the printing of the input image data stored therein is completed.
Suppose that a date is to be printed in red on a black-and-white document. In this case, a page memory corresponding to the black component is acquired based on the size of the input image data and the color component which is black. Hence, when printing the document, the black component of the input image data is developed in the acquired page memory and the black component can be printed, but the date cannot be printed in red because no page memory is yet acquired for the red component. In order to print the red component of the input image data, it is necessary to acquire the page memory therefor and develop the red component of the input image data in acquired the page memory.
There is no problem in printing the date in red, that is, the red component of the input image data, if the page memory has a sufficiently large storage capacity. However, if the storage capacity of the page memory is small, the page memory will become full by storing the black component of the input image data, and it will be impossible to acquire the necessary storage capacity to store the red component of the input image data in the page memory. This means that the required page memory resource cannot be acquired, and that the print job cannot be executed. On the other hand, if the secondary storage unit such as the HDD is provided in the image forming apparatus, even when the storage capacity of the page memory is small, the black component of the input image data stored in the page memory can be saved temporarily in the secondary storage unit such as the HDD to make the page memory available for storing the red component of the input image data.